Viscous fluid shear clutches and control valves therefor

ABSTRACT

A viscous fluid shear clutch comprises a two-part outer casing 14,15 and an inner clutch member 10 between which is defined a clearance gap into which viscous fluid may flow to provide an adjustable degree of coupling between the casing and the clutch members. Fluid is continually pumped out of the gap by a circumferential scoop pummp. The clutch may be assembled for reverse operation by indexing the casing parts relative to one another. The quantity of fluid in the gap may be controlled dependent on sensed temperature and sensed speed or sensed temperature alone. A thermo pressure valve provides a pressure force related to the sensed temperature; this relationship may be inverse for failsafe operation.

This is a division of application Ser. No. 08/006,733, filed on Jan. 21,1993 (now abandoned); which is a division of application Ser. No.07/717,611, filed Jun. 19, 1991 (now U.S. Pat. No. 5,191,915); which isa division of application Ser. No. 07/461,535, filed Jan. 5, 1990, (nowU.S. Pat. No. 5,042,629).

This invention relates to viscous fluid shear clutches and controlvalves for use in such clutches.

There are many known forms of viscous fluid clutch for providing drivebetween an engine and a cooling fan which incorporate arrangements whichsense the coolant air temperature and/or the output speed of the clutchand modulate the degree of coupling between the input and outputaccordingly. However, many systems experience severe hysteresis whichmeans that, in practice, the coolant is either overcooled--representinga needless waste of engine power--or undercooled--leading to possibleengine damage.

A need exists for a viscous fluid clutch in which the modulation of thedrive to the fan is performed with less hysteresis, thus providingimproved engine efficiency.

Most known forms of viscous fluid shear clutch employ a scoop pumparrangement in which the scoops face an axial end face of the innerclutch member--so called "side scoop" arrangements. Such arrangementsrequire careful and precise alignment of the scoop and the opposingworking face of the clutch member and this can be difficult to achieveand time consuming because of axial float of the shaft. Thus the lowestclearances possible between the scoop and the clutch member still leavesignificant leakage oaths which reduce the efficiency of t he scooppumps. Also, in such arrangements even when the clutch is drained thereis still a significant degree of coupling because the scoops are on theside of the clutch member.

A need exists for a viscous fluid shear clutch incorporating a pumpingarrangement which provides good pumping efficiency, may be assembledeasily, and which allows the clearance gap between the drive members tobe substantially "dry".

A need also exists for a viscous fluid shear clutch which can beassembled for either clockwise or anticlockwise rotation with little orno modification necessary to the component parts.

A need also exists for a viscous fluid shear clutch in which the clutchprovides full coupling if the temperature signal is lost.

Accordingly, in one aspect this invention provides 9 viscous fluid shearclutch for providing drive between an engine and a cooling fan, saidclutch comprising:

a rotary casing,

an inner clutch member within t he casing and spaced therefrom by aclearance gap,

a fluid reservoir communicating with said clearance gap,

pump means arranged to pump fluid from the clearance gap to thereservoir in response to relative rotation between the casing and theinner clutch member,

valve means arranged to control the flow of fluid between the pump meansand the clearance gap and including a movable control element,

thermal sensor means including a remote sensor for sensing thetemperature of a coolant fluid and a separate actuator for generating atemperature dependent force which acts upon said movable controlelement,

speed sensor means for centrifugally generating a speed dependent forcewhich acts upon said movable control element whereby an increase in thesensed temperature or a decrease in the sensed speed tends to adjust thevalve means to increase the fluid in the clearance gap.

Preferably, said thermal sensor means is arranged to provide atemperature dependent force which decreases with an increase intemperature, thereby to provide a failsafe feature.

Preferably, said pump means is constituted by a generally plaincircumferential wall portion of said inner clutch member and at leastone circumferentially extending scoop of limited arcuate extent providedin a opposed cylindrical wall of the casing, each scoop havingassociated therewith a scoop pump outlet passage arranged adjacent theend region of the which trails in the sense of rotation of the scooprelative to the inner clutch member.

To allow assembly for rotation in either sense, said rotary casingpreferably includes one part defining at least a major portion of eachscoop and another part defining at least a major portion of each scooppump outlet passage, the two parts being capable of being assembled ineither one of two relative angular positions whereby each scoop pumpoutlet passage can be located at either end region of the associatedscoop depending on the intended sense of rotation of the clutch.

The thermal sensor means may include:

a thermo pressure valve having a valve body defining an inlet for servofluid, an outlet for connection to said actuator, and a vent,

shuttle spool means linearly movable within said body between a firstposition, which allows communication between said inlet and said outlet,and a second position which allows communication between said outlet andsaid vent, and

a sensor element responsive to the sensed temperature for moving saidshuttle spool means.

The shuttle spool means preferably isolates both said inlet and saidvent from said outlet when it is in an intermediate position.

The shuttle spool means is preferably provided at spaced regions withseal surface means engageable in resilient sealing manner withrespective valve seats in said valve body and the spacing between saidseal surface means may be set as required. Each seal surface means maycomprise a resilient `0` ring.

Preferably movement of said shuttle spool means away from said internedlate position causes resilient compression of one of said `O` ringsagainst its valve seat and lifting of the other `O` ring from its valveseat.

In another aspect, this invention provides a three way valve comprisinga valve body defining three inlet/outlet means and a shuttle spool meanslinearly movable in said body between a position which allowscommunication between said first and second inlet/outlet means, and aposition which allows communication between said first and thirdinlet/outlet means.

In another aspect, this invention provides a valve arrangement includinga valve body defining an outlet port and at least two inlet ports eachfor receiving fluid at respective pressures, a shuttle spool meanscontrolling the flow between said inlet and outlet ports and movablebetween one position in which one of said inlet ports communicates withsaid outlet port, and another position in which the other of said inletports communicates with said outlet port, wherein means are provided formoving said shuttle spool between said aforementioned positionsdependent on at least one of said given pressures.

The invention may be performed in various ways and certain embodimentsthereof will now be described by way of example only, reference beingmade to the accompanying drawings, in which

FIG. 1 is a cranked sectional view through a viscous fluid shear clutchin accordance with this invention;

FIGS. 2a and 2b are transverse sectional views on lines II--II of theclutch of FIG. 1, showing the clutch when configured for clockwiserotation of the inner clutch member and anticlockwise rotation thereof,respectively;

FIG. 3 is an end view on the rear housing of the clutch taken in thedirection of arrows III--III of FIG. 1;

FIGS. 4a 4b and 4c are detail views of three modified controlarrangements for a clutch of the general type illustrated in FIG. 1,

FIGS. 5a and 5b are section views of two examples of thermal pressurevalve for supplying a temperature dependant pressure signal to theactuator of the clutch of FIG. 1, and

FIG. 6 is a schematic view of a dual temperature thermal pressure valvesystem for supplying a pressure signal to a viscous fluid shear clutch.

Referring to FIGS. 1 to 3, the invention is applied to a viscous fluidclutch of the general type including an internal clutch member or rotor10 connected to and driven by a coupling 12 attached to an engine shaft(not shown). The rotor is positioned within a two part casing having afront part 14 and a rear part 15. A bearing 16 supports the rear part ofthe casing off the coupling 12 or shaft. In this example, the casingincludes-threaded studs 17 which support the blades of a fan (notshown). The rotor 10 has a series of closely spaced annular rings 18respectively located in a series of grooves 20 in the front and rearparts 14 and 15 of the casing to define a labyrinthine clearance gap ofconsiderably extended area across which torque may be transmitted byviscous shear forces. The amount of torque transmitted may be increasedor decreased by increasing (filling) or decreasing (draining) the amountof viscous hydraulic fluid in the gap.

A fluid reservoir 22 is formed between the front casing part 14 and aninternal partition wall 24 and fluid is continuously pumped from theclearance gap to the reservoir by diametrically opposed pumparrangements 25. Each pump arrangement 25 comprises an arcuate scoop 26formed in the rear casing part 15 and spaced closely from the outercircumferential periphery of the internal rotor 10. On rotation of therotor 10, viscous fluid adjacent each scoop 26 is entrained by the rotorand drawn towards an outlet port 28 in the end of the scoop that trailsin the sense of the rotation of the scoop relative to the rotor. Fluidpumped from ports 28 passes to the reservoir 22 via respective radialpassages 30. The assembly of the clutch for clockwise and anticlockwiserotation will be discussed below in relation to FIGS. 2 and 3.

Fluid in the reservoir 22 may drain back to the clearance gap via one ormore valve openings (one, 32 shown in the drawings) which is opened orclosed by a valve blade 34 forming an extension of a control element 36pivotted at 38 to tile partition wall 24. The control element includesan enlarged portion 40 which acts as a bob weight and is disposedrelative to the pivot 38 so that the centrifugal force generated onrotation of the casing tends to urge the control element 36 to close thevalve opening 32. Closing movement of the control element 36 is resistedby a compression spring 42 located between the control element 36 andthe partition wall 24.

An actuator in the form of a pressure ram assembly 44 rotationallyisolated from the casing by a bearing 46 includes an axially movable ram48 provided with a rotationally isolated button 50 engageable with thecontrol element. The pressure ram assembly 44 is supplied with apressure signal from a thermal pressure valve of the form illustrated inFIG. 5(a) and to be described in detail below. The pressure signaldecreases as the sensed temperature increases.

In operation, the pump arrangements 25 continually pump fluid from theclearance gap to the reservoir and flow between the reservoir and thegap is controlled dependent on both the engine coolant liquidtemperature and the output speed of the clutch--i.e. the rotationalspeed of the casing 14,15. Both the speed dependent force and t hetemperature dependent force act in the same sense, tending to move thecontrol element 36 to close the aperture 32 in the partition wall 24,and these forces are opposed by the spring 42. An increase in the sensedtemperature reduces the pressure signal applied to the ram assembly, sothe control element 36 tends to open the aperture 32, thus increasingfluid in the clearance gap. Likewise, a reduction in the rotation speedof the casing and thus the fan--reduces the centrifugal force opposingthe spring 42, so again tending to open the aperture and increase fluidin the gap.

An important feature of this arrangement is that if the pressure supplyto the pressure ram assembly fails for any reason, the control element36 will tend to open the aperture thus flooding the clearance gap withfluid to ensure that drive between the fan and the engine is preserved.

Another important feature is that the arrangement allows continuousmodulation of fan speed versus coolant temperature across substantiallythe whole operating temperature range.

A further advantage is that the balance of a temperature dependent forceagainst a centrifugally generated speed dependent force provides reducedhysteresis when the sensed temperature falls, because the speed forcevaries as the square of the speed. Also, the fan speed versus coolanttemperature characteristics can be predicted reasonably accuratelybecause the temperature/force characteristic of the thermal pressurevalve and the speed/force characteristic of the speed sensor can bepredicted mathematically.

This leads to a significant improvement of the efficiency of the coolingsystem because it allows the fan speed to be tied more closely with thecoolant temperature (i.e. the cooling requirement) so that the problemsof wasting engine energy by overcooling or risking engine damage byoverheating are avoided.

Referring now to FIGS. 2a, 2b and 3, the casing parts 14,15 of theclutch of FIG. 1 are configured so that they can be assembled for enginerotation in either the clockwise sense (FIG. 2a ) or anticlockwise sense(FIG. 2b). For proper operation of the scoop pumps, the dump outletpassages or ports 28 must be in the trailing end of the scoops 26, asmentioned above, and so the layout of the scoops 26 and ports 28 must bechanged for rotation in the opposite sense. This is achieved in thepresent arrangement by providing the scoops 26 in the rear casing part15 and the outlet port and passages in the front casing part anddesigning the arcuate extent of the scoops and the gaps therebetween inrelation to the pitch of the bolts 43 which secure the casing togetherso that the "handedness" of the clutch can be switched simply byindexing the front and rear casing parts by one bolt spacing.

For ease of assembly during manufacture, the front casing part includesa notch mark 47 and the rear casing part includes the letters `A` and`C` which should be lined up with the mark to denote anticlockwise orclockwise rotation respectively.

FIGS. 4a, 4b and 4c show detail views of three alternative forms ofcontrol arrangement for being acted upon by a pressure rain assembly 44and for controlling the flow through the aperture 32. Each arrangementis similar in some aspects to that of FIG. 1 so common referencenumerals have been used where appropriate.

FIG. 4(a) shows an "open loop" arrangement in which the temperaturedependent force supplied by the assembly 44 is the only active controlforce applied to the control member 36; there is no speed dependentcontrol force as the relevant inertias of the control member 36 arebalanced about the pivot point 38. The temperature dependent force isresisted by a spring 42, and increases as the sensed temperaturedecreases.

FIG. 4b shows a "closed loop" arrangement in which a thermal pressurevalve of the form illustrated in FIG. 5b below provides a temperaturedependent force which increases with an increase in temperature. Thepressure from the assembly is applied via a common yoke assembly 59, tothe ends of two cocking control members 54,56, one of which, the mastercontrol member 54 has a valve blade 34 cooperating with the aperture 32.Each of the control members has a bob weight portion 52 whichcentrifugally generates a force which opposes the temperature dependentforce applied by the assembly 44. An increase in sensed temperature or adecrease in the speed of the casing tends to adjust the master controlmember 49 to increase the fluid in the clearance gap.

FIG. 4(c) shows another "closed loop" arrangement in which a thermalpressure valve of the form illustrated in FIG. 5(b) provides atemperature dependent force which increases with an increase intemperature. The temperature dependent force is counteracted by a speeddependent force provided by a piston 60 acted upon by the pressuregenerated by one of the circumferential scoop pumps 25. The pressuregenerated by the scoop pump decreases with an increase in differentialspeed between the outer casing and the inner clutch member so that,assuming a constant input speed, the scoop pump pressure increases withrotational speed of the casing.

Referring now to FIGS. 5(a) and 5(b), two forms of thermo pressure valveare illustrated, one (FIG. 5a) providing a pressure signal whichdecreases with an increase in temperature and the other (FIG. 5b)providing a pressure signal which increases therewith.

The valve of FIG. 5(a) comprises a valve body 66 which defines an inlet68, an outlet 70, and a vent 72. A shuttle spool 74 is mounted in thebody and includes at each end region an `O` ring 75,76 which engages arespective chamfered valve seat 77,78 provided within the valve body.The shuttle spool 74 is made of two parts 71,73 threaded together whichallow the spacing between the `O` rings to be adjusted. In use, thevalve is adjusted so that, when in the equilibrium or intermediateposition of the shuttle spool 74, both `O` rings seal against theirvalve seats so that there is no communication between any of the inlet68, outlet 70 and vent 72. Shifting of the shuttle spool 74 to the left,as viewed in FIG. 5a, will compress the `O` ring seal 76 against thevalve seat 78, thus maintaining the seal between the inlet 68 and theoutlet 70, whilst at the same time lifting the `O` ring 75 off the valvegear 77 so allowing flow between the outlet 70 and the vent 72.Likewise, rightward shifting of the shuttle spool 74 allows flow betweenthe inlet 68 and the outlet 70, whilst preventing flow between theoutlet 70 and the vent 72.

At one end, the shuttle spool 74 is connected via a spring to theactuator rod 30 of a thermal sensor 82 such as a wax capsule, whichsenses the temperature of the engine coolant. The temperature/pressurecharacteristics of the thermo valve can be biassed by turning anadjustable cap 34 which applies an adjustable biass force via a spring85 to the left hand end of the shuttle spool 74.

The valve of FIG. 5(b) operates in the reverse sense, i.e. the outputpressure increases with sensed temperature, but the components aresimilar in form and have been given common reference numbers. In thisarrangement biass adjustment may be effected by turning the thermalsensor housing 88.

Apart from at lower temperatures of the operating range, both valvesmodulate the pressure substantially linearly with sensed temperature.

FIG. 6 shows schematically a dual temperature thermal pressure valvesystem which responds to two different temperatures. In the exampleshown, the valve responds both to the intercooler temperature and to theengine coolant temperature. Both temperatures are sensed bythermopressure valves 90,92 respectively of the form shown in FIG.5(b)--i.e. which provide an increase in, the output pressure as thesensed temperature increases. The temperature modulated pressure signalsare supplied to a combinet valve 94 which comprises a body 96 definingleft-hand, central and right hand chambers 97,98,99, respectively.

The central chamber 98 includes a shuttle spool 100 with two `O` rings101, 102 which seal against valve seats 103,104 in the valve body whenthe shuttle spool is in an intermediate position. Each of the otherchamber includes a piston 196 having a push rod for engaging the shuttlevalve 100. The output pressure signal is taken from the central chamber,between the two valve seats 103, 104. The engine coolant modulatedpressure signal is supplied to the right hand chamber 99 and the lefthand end of the central chamber. The intercooler moderate temperature issupplied to the left hand chamber 97, and t he right hand end of t hecentral chamber.

In use the combine valve 94 provides a combined pressure signal to theclutch which is modulated in accordance with both the intercoolertemperature and the engine temperature. In practice, the system could beset up so that the fan runs at an idle speed of 150 rpm when there is nocooling demand from either the intercooler or the engine coolant. Whenthe intercooler signals a demand the system may supply a controlpressure which causes the fan to run at, say, 800 rpm. This may be asimple on-off control or there may be continuous modulation up to 800rpm. When the engine coolant signals a demand the system may supply apressure signal which modulates the fan output speed in accordance withtemperature from 800 rpm to just below the engine speed. The above formsof clutch automatically vary the output speed of the casing 14/15 inaccordance with the sensed temperature. The clutch may be modified toadjust the output speed as required by a user, i.e. by providing someform of pressure control for controlling the pressure supplied to theram.

In the above examples of viscous clutch the force applied via assembly44 is hydraulically generated; it could of course be generated in otherways, for example by an electrical force transducer.

Likewise, in the above examples of thermo-pressure valve, the forcesignal applied by the wax capsule could be applied by a force transducerand could represent a variable other than sensed temperature.

I claim:
 1. A pressure modulator valve for modulating an output pressurein response to a sensed parameter, comprising:a body having first,second and third ports respectively defining a modulated output pressureport, a fluid supply pressure port and a vent; a shuttle spool meansmovably mounted in said body; two spaced alternately openable flowcontrol zones disposed one intermediate said first and second ports andone intermediate said first and third ports, for controlling the flowtherebetween; each flow control zone comprising annular seal means ofresilient material associated with one of said shuttle spool means andsaid body for cooperating with seal surface means, the other of saidshuttle spool means and said body having seal surface means forcooperating with said annular seal means, each said annular seal meanspreventing the respective cooperating seal surface from moving beyondsaid annular seal means, thereby constraining movement of said shuttlespool means with respect to said body, so that movement of said shuttlespool means in one sense causes said seal surface means in one flowcontrol zone sealingly to displace the associated annular seal means andcauses the seal surface means in the other flow control zone to lift offthe associated annular seal means to thereby open that flow controlzone, whereby movement of said shuttle spool means in one sense causessaid first port to be in communication with said second port, andmovement in an opposed sense causes said first port to be incommunication with said third port, wherein at least one of said bodyand said shuttle spool means comprises two parts adjustably engaged witheach other to allow an adjustable pre-load to be applied to said annularseal means.
 2. A pressure modulator valve according to claim 1 whereinsaid shuttle spool means is movable to an intermediate position in whichsaid first port is isolated from both said second and third ports.
 3. Apressure modulator valve according to claim 1 for modulating an outputpressure at said first port, wherein said second port is connected inuse to a source of fluid pressure and said third port is connected inuse to a vent, and wherein transducer means is provided for moving saidshuttle spool means in response to a sensed parameter.
 4. A pressuremodulator valve according to claim 3 wherein said transducer comprises aforce transducer.
 5. A pressure modulator valve according to claim 1wherein said annular seal means comprise axially `O` ring seals providedon said shuttle spool means, and said seal surface means compriseoppositely facing tapered valve seats on said body.
 6. A pressuremodulator valve according to claim 5 wherein said shuttle spool meansincludes means for allowing adjustment of the axial spacing of the `O`ring seals.